1. Field of the Invention
The present invention relates to key locking devices and, more particularly, to expandable key locking devices for locking and coupling a first part to a mating second part.
2. Prior Art
The problem of connecting mating male and female parts, such as for example connecting shafts to mating gears or pulleys, in order to transfer torques and/or axial forces between the mated male and female parts has been one of the immutable engineering problems. Accordingly, many efforts have been expended to find a satisfactory solution to this problem. Some of the solutions tried in the prior art include providing either or both the male and female parts with bolting flanges which are mechanically fastened to surfaces of the mating part seated on the flange. Bolting flanges, however, significantly increase the size and weight of the connection between parts, and thus, are not satisfactory for applications where size, weight, and cost are critical. Another well know attempt at solving the problem of connecting the male and female parts uses keys, such as square keys or Woodruff keys, housed in keyways machined or otherwise formed in both the male and female parts. The keys act in shear to transfer torque and axial loads between mated male and female parts. Use of keyed connections generally does away with the bulk and weight of flanged connections, but in turn requires machining of close tolerance keyways into both the male and female parts which is both costly and time consuming. They are frequently insufficiently accurate and subject to failure, as it is virtually impossible to get zero play. Reversing loads beat up traditional keys and destroy them. Furthermore, the keyways formed into both the male and female parts reduce the effective cross-sectional area of the parts, and have square corners that raise stresses thereby having a weakening effect on the parts. In addition, some keys may have to be fastened to one of the parts with set screws to prevent the keys from exiting the keyways during use. This requires a hub, creating additional size and weight to accommodate the set screw. Fabrication of the set screw holes and installation of the set screw further increases the cost and complexity of the keyed connections. Still another solution of the prior art attempts to eliminate the problems with flanged connections and keyed connections by using keyless bushings or expandable keys to connect the mating male and female parts. The keyless bushings of the prior art generally have inner and outer tapered sections which when clamped together generate radial pressure that locks the mated parts together. One example is U.S. Pat. No. 3,849,014 which discloses an expandable hub locking assembly with inner and outer annular hub parts which have slidably engaging frustoconical surfaces interconnected by three screws. Rotation of the screws causes sliding engagement of the frustoconical surfaces which produces radial contraction and expansion of the inner and outer hub parts onto the shaft and bore. Another example is U.S. Pat. No. 3,841,774 which discloses an expandable shaft key having first and second key parts which slidably engage each other along sloping surfaces and are connected by a threaded rod. The keyless bushing or expanding keys of the prior art are generally large in size in order to provide large contact surfaces for gripping the male and female parts. The keyless bushing is standard in the industry where designers require extremely large clamping forces. Because of their limited ability to grab onto the shaft, and their increased ability to force the hub, the forces have a propensity to split the hub. The keyless bushings also slip or translate axially when tightening the screw. The present invention overcomes the limitations and problems of the prior by providing a small, inexpensive key which may be used without keyways to effectively lock male and female parts together to simultaneously transfer both torques and axial loads therebetween. If keyways are used, modern end-milling methods are far faster, far more economical and far more accurate than those used by traditional keys. The device of the present invention does not suffer from installation play, allows larger tolerances when machining keyways, and has significantly more surface contact. The device of the present invention is vibration proof and easily removed. Also they may be ganged axially or circumferentially. Furthermore, the keyway of the present invention may be readily cut with a standard drill and drill press along with an inexpensive drill jig that has been designed for this purpose.
In accordance with a first embodiment of the present invention, a coupling device for coupling a first part to a second mating part is provided. The coupling device comprises a fastener, a distal member, and an intermediate member. The fastener has a support shoulder extending radially from the fastener. The distal member is movably engaged to the fastener to move relative to the fastener along a longitudinal axis of the fastener when the fastener is turned relative to the distal member. The intermediate member is disposed on the fastener between the distal member and support shoulder of the fastener. When the distal member is moved towards the support shoulder on the fastener, the distal member is biased against the intermediate member for effecting outward expansion of the coupling device relative to the longitudinal axis of the fastener. Thus, the coupling device is an assembly comprising of three congruently shaped axially extending parts with mating wedge-like angular cuts intended to cause said parts to expand in a direction of the minor width when a screw type fastener pulls the two outer members together. Those angular surfaces are made so the parts do not permanently lock up, thereby allowing the device to be removed and re-used. The angles may be equal so the parts stay in place axially when the screw is tightened.
In accordance with a second embodiment of the present invention, a mechanical connection between a first part and a second mating part is provided. The first part has an inner opening into which a mating portion of the second mating part is located. The mechanical connection between the first and second parts is provided by an expandable coupling positioned between an inner surface of the inner opening of the first part and the mating portion of the second part. The expandable coupling comprises a fastener with a support shoulder thereon. The expandable coupling also has an end member threadably mounted on the fastener, and an intermediate member mounted on the fastener between the support shoulder and the end member. When the fastener is threaded into the end member, the end member is biased against the intermediate member causing an outer surface of the intermediate member to be displaced outward relative to the fastener and effecting expansion of the expandable coupling.
In accordance with a third embodiment of the present invention, a key assembly for connecting a first part to a mating second part is provided. The key assembly comprises a fastener, a first wedge section connected to the fastener, a second wedge section connected the fastener, and a third wedge section connected to the fastener. The third wedge section is disposed between the first and second wedge sections. When the first and second wedge sections are drawn together with the fastener, the third wedge section is cammed outwards relative to the longitudinal axis of the fastener. The fastener holds the first wedge and the second wedge together so that the key assembly is expanded.